1. Field
One or more aspects of embodiments of the present disclosure relates to a separator for a rechargeable battery and a rechargeable battery including the same.
2. Description of the Related Art
As electronic devices continue to decrease in weight and size, the rechargeable batteries that serve as power sources for these electronic devices are also required to have high capacities, lower weights, smaller sizes (e.g., form factors), and/or the like. Rechargeable lithium ion batteries have beneficial features such as high voltage, long cycle-life, high energy densities, and/or the like. Therefore, rechargeable lithium ion batteries are an area of active research, manufacturing, and sales.
The characteristics of a rechargeable lithium battery may be largely affected by the characteristics of its electrodes, electrolyte solution, other battery materials, and/or the like. For example, the separator for the rechargeable lithium ion battery may have an influence on the cycling characteristics of the rechargeable lithium ion battery.
The separator may be manufactured by coating a slurry including inorganic particles and a binder on a porous substrate.
Such a separator may be called a coating separator due to the presence of the coating layer including inorganic particles and binder on the porous substrate. The binder may facilitate bonding between the inorganic particles and a porous polyethylene film and/or facilitate bonding between the inorganic particles and other inorganic particles. When this separator is used to manufacture a rechargeable lithium ion battery, the cycling characteristics of the rechargeable lithium ion battery may be affected by the characteristics of the binder used to bond porous polyethylene (PE) with ceramic particles (e.g., the inorganic particles) as well as the ceramic particles themselves.
In some embodiments, when ceramic particles having high heat resistance are used to form the coating layer, a battery having high voltage and high-capacity characteristics may be manufactured. The ceramic particles having high heat-resistance may be able to sufficiently exert their characteristics when the binder stably maintains the structure of the ceramic coating layer during charge and discharge of the rechargeable lithium ion battery. In other words, the highly heat-resistant ceramic particles need to be stably maintained inside the separator. In addition, the binder needs to firmly bond the separator with each electrode. Accordingly, a binder having excellent heat resistance and adherence is required.
Currently, research on binders for coating separator is sparse, but binders used in electrodes have been used as binders for the coating separator. For example, a representative electrode binder composition (hereinafter referred to as a PVDF-based binder) obtained by mixing a polyvinylidene fluoride (PVDF)-based polymer with an organic solvent such as N-methyl-2-pyrrolidone (NMP) and/or the like may be used as the binder for a coating separator. However, the PVDF-based binder needs to be used in an excessive amount for the separator to maintain sufficient adherence, and the resulting structure of the coating layer is unstable due to impregnation of the electrolyte solution and mass transfer of lithium ions during charge and discharge of a rechargeable lithium ion battery.
In order to solve this problem, a method of improving adherence between an inorganic oxide (a kind of inorganic particle) and porous polyethylene (PE) using a binder having a strong adherence chemical structure, and a silane coupling agent has been suggested. Another method using an IPN (interpenetrating polymer network)-type or kind of resin obtained by polymerizing a PVDF-based polymer and a hydrophilic polymer (unsaturated carboxylic acid) and/or the like has also been suggested.
A separator having a porous coating layer formed as a mixture of inorganic particles (e.g., BaTiO3 or Al2O3) and a binder polymer (e.g., butyl acrylate or a copolymer of acrylonitrile and acrylic acid) on a surface of a porous substrate and a rechargeable lithium battery using the separator have been previously disclosed.
However, the aforementioned binder exhibits adherence to either one of the porous PE or the inorganic particles, but has no sufficient (e.g., no substantial) adherence to both of them.
Accordingly, a coating separator formed of this binder undergoes structural changes during extended charge/discharge cycling of the rechargeable lithium ion battery, which shows deteriorating battery capacity.
The information disclosed in this Background section is included only to enhance understanding of the background of the present disclosure, and may therefore contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.